Corporate information processing systems and data centers have come to possess growing numbers of servers, incurring the concomitant increase in the cost of server operation and management.
In order to solve this problem, there exist known techniques for virtualizing servers. The server virtualization techniques involve getting a single physical server to operate a plurality of virtual servers. Specifically, the processor (CPU), memory, and other resources of the physical server are divided, and the divided resources of the physical server are assigned to a plurality of virtual servers. And the multiple servers operate concurrently on one physical server. The virtualized servers possess virtual hardware resources, and are each assigned an amount of the divided physical server resources. In this manner, virtualized servers are operated collectively on the physical server, whereby the increase in the number of servers is minimized. In order to reduce costs, it is necessary to boost the degree of server aggregation.
A virtual hard disk is for use by a virtual server, and some virtual hard disks are handled as files on the physical server (on a virtualizing program) for enhanced operability. The virtual hard disk files include virtual hard disks of a fixed type which have the same disk size as the virtual hard disks when created, and virtual hard disks of a variable type which have their file size varied depending on the volume use size on the virtual hard disks. In the case of the variable type, the volume is not appropriated only once by the disk size, so that the degree of aggregation can be enhanced.
There exist similar storage virtualization techniques for assigning to the server a volume larger than the actual physical volume. The storage virtualization techniques also involve reducing costs by boosting the degree of aggregation in a manner similar to virtual hard disk files of the virtual type. As described In Patent Literature 1 below, it is possible to virtualize the storage volume so as to assign to the server a storage volume larger than the actual storage volume.